Building In-Ground Hot Tub

[EarlyPorsche]

Been floating the idea of building a concrete in-ground hot tub. I have natural gas right next to this location. There seems to be tons of info on the web but I can't tell what is good. Figured I would ask here where a couple people probably have done this. Main questions are:
1. how thick should my walls be poured?
2. what is a good gas heater brand
3. what is a good brand for the pump for the jets
4. any tips on plumbing it all together

[red-beard]

I have a 7' x 7' hot tub, built as part of my pool. Walls are gunnite, same thickness as the pool. I think they were 4-6" and had rebar. The seat comes 18" from the wall which leaves a 4'x4' section in the middle. The depth in the middle is 3' and the seat is 18" high.

I like Hayward parts, mostly because it's what I have and they seem to work. Options for heater were 120kBTU/hr or 400kBTU/hr. We went with 400 since it heats the hot tub faster and the pool (27000 gallons) if needed. 400kBTU/hr will raise my pool 2 degrees per hour. My Hot tub is roughly 1000 gallons. The Heater will heat that around 50 degrees per hour.

[dad911]

Year round? Weather? Where are you located?

For my point, 10" concrete, attached to pool, but we also have a separate fiberglass (electric-self contained, heavily insulated) we use year round.

Concrete spa more social when we use the pool, but the fiberglass one is more versatile, more comfortable (more jets, more adjustable)

[Cajundaddy]

I used to install a bunch of in-ground spas back in my youth. At this point I can't recommend a stand-alone concrete spa. The best portable spas are just better in every way. Always clean, always at desired temp, jet options beyond belief, and much more comfortable seating. If you want it to be a focal point in the backyard that you might use occasionally, an in-ground still may make sense. If you want ease of ownership and more Porsche than GMC experience, take a good look at Hot Spring, Caldera, and Sundance spas. You can still build them into a deck and get an in-ground look with all the benefits of fully self contained.

No current affiliation but I owned a spa dealership for 20 years:
Hot Tub Information - How to Buy a Hot Tub | Hot Spring Spas

[EarlyPorsche]

So I am outside of DC - so total midatlantic. Would use year round. The house really couldn't take a fiberglass - needs to be built in concrete or nothing.

I am thinking 4-6" walls with rebar. Pebbletech or something like that interior.

12" above the patio with a flagstone lip to sit on.

In terms of jets - can one just put threaded PVC into the concrete and then thread the jets in? I am unclear on how that end works. Planning now and hopefully starting in the late fall.

[scottmandue]

Originally Posted by Cajundaddy

I used to install a bunch of in-ground spas back in my youth. At this point I can't recommend a stand-alone concrete spa. The best portable spas are just better in every way. Always clean, always at desired temp, jet options beyond belief, and much more comfortable seating. If you want it to be a focal point in the backyard that you might use occasionally, an in-ground still may make sense. If you want ease of ownership and more Porsche than GMC experience, take a good look at Hot Spring, Caldera, and Sundance spas. You can still build them into a deck and get an in-ground look with all the benefits of fully self contained.

No current affiliation but I owned a spa dealership for 20 years:
Hot Tub Information - How to Buy a Hot Tub | Hot Spring Spas

Thank you, I'm think of doing something like this... except we have an indoor storage space (if I can ever clear it out) and maybe would install it in there... great for privacy and safety (don't have to worry about kids getting into it. do you think the weight would crack a ordinary slab floor?

[greglepore]

Cajundaddy has the right idea. Inground will be near small pool cost-its gunitte and rebar, not poured. I did a 10x10 for a friend maybe 10 yrs ago, was a major undertaking. Something to consider is that many spas get tons of use the first year and minimal after that-you can eliminate an above ground, not so with a gunnite spa. Build a fiberglass spa into deck or hardscape.

I'd add Dimension One to the list of spas above, mine is 15 yrs young and aside from some basic repairs has been trouble free, and looks great.

[Cajundaddy]

Originally Posted by EarlyPorsche

So I am outside of DC - so total midatlantic. Would use year round. The house really couldn't take a fiberglass - needs to be built in concrete or nothing.

I am thinking 4-6" walls with rebar. Pebbletech or something like that interior.

12" above the patio with a flagstone lip to sit on.

In terms of jets - can one just put threaded PVC into the concrete and then thread the jets in? I am unclear on how that end works. Planning now and hopefully starting in the late fall.

I don't understand this statement : "The house really couldn't take a fiberglass - needs to be built in concrete or nothing."

This is what I meant by taking a fully self contained spa and building it into a deck. In-ground concrete look, most excellent spa ownership benefits:


Here is one installed with a flagstone seat. The spa always stays covered of course so the only time you actually see the shell is at night when you get in.


If that is not something you would consider, figure $4k for heater, equip, and controls, plus all construction, concrete, and plumbing costs. $8-15k total depending on your wants.

Jet plumbing needs to be balanced for rated psi and gpm. Each jet has a water and air line that connect at a venturi. Figure out how many jets, optimum gpm per jet, distance to equipment pad, plumbing line sizes, calculate total head loss, and then choose a pump that will reasonably provide the needed gpm at calculated head loss. It's not like rebuilding a GT3 motor but a lot more involved than just screwing the jets into threaded fittings at the wall. Like mechanics, anyone can learn this trade but it will require lots of homework.

I recommend pondering this question further. A well-engineered portable spa install can be made to look any way you want it to look. Flagstone, cantilever decking, natural stone, the only limitation is your imagination. The difference is in real everyday use a portable from a major mfg has a lot more to offer than anything I could build with concrete... And I have built quite a few.

[john70t]

You are in a freeze/thaw zone.

One problem might be the drainage system:
-The cover accidentally stays off for a couple months while you're out of town. Under the maples in the fall.
-The neighborhood kids decide to dump a bag of concrete in the thing after you catch them.
What next?

[ckelly78z]

For less than 10K, you can get one of the best and nicest hot tubs out there, and have low maintenance, and heating costs as well. I bought a HOT SPRINGS 5 person spa 25 years ago and have only changed out the cover twice and the heater once (it froze while moving in the Winter). This tub is a fully sealed/insulated stand alone that can be put anywhere it can sit level, and the it never costs more thgan about $25 to heat in the coldest month. We only use it below about 50 degrees air temperature.

[Cajundaddy]

Originally Posted by scottmandue

Thank you, I'm think of doing something like this... except we have an indoor storage space (if I can ever clear it out) and maybe would install it in there... great for privacy and safety (don't have to worry about kids getting into it. do you think the weight would crack a ordinary slab floor?

A typical concrete foundation is usually fine. If you like, have these guys come and do a site inspection to see what fits best into your plans. I have been out of it for 10 years but they were one of the best in the biz.
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